The present invention generally pertains to optical scanning systems and is particularly directed to a scanning system for scanning a code symbol consisting of a combination of spaced parallel bars affixed to an object for providing coded information related to the object.
A typical scanning system of this type includes a housing and/or a panel for defining a scanning region adjacent the housing or panel for receiving objects having the code symbol, a light source, such as a laser, for providing a light beam; an optical system for scanning the light beam in a predetermined pattern throughout the defined scanning region; and a detection system for detecting light having at least a predetermined intensity reflected from the code symbol and for providing an electrical signal in response to detection of such reflected light; and an optical system for directing light from the scanned light beam that is reflected from the code symbol on a received object to the detection system.
These systems are useful in reading bar code symbols such as the Universal Product Code (UPC) code symbols that are affixed to many packaged grocery items. UPC code symbols consist of parallel bars having various widths and spacings. The electrical signals provided by the detection system in response to scanning the code symbol are provided to a data processing system which provides various functions in relation to the information represented by the electrical signal, such as registering and displaying the price of the item bearing the code symbol and adjusting inventory records concerning such items.
An important consideration in using scanning systems of this type is the orientation of the code symbol within the scanning region defined by the panel so as to enable the full code symbol to be scanned by the light beam. In many prior art scanning systems the code symbol must be precisely oriented within the defined scanning region in relation to the panel. The time consumed in precisely aligning the code symbol delays the scanning of a large number of items. This is a distinct disadvantage to using such a scanning system in locations such as a supermarket checkout counter where it is desirable to scan a large number of code symbols rapidly. Although there are some prior art systems that do not require precise orientation, these systems have not proven to be wholly satisfactory because of various problems, such as there being holes in the scanning pattern, the depth of field in which the object must be received being shallow, and/or the orientation being limited to a relatively small angle in relation to a given direction.
In one prior system that does not require precise orientation, the panel which defines the scanning region for receiving objects bearing a code symbol includes light transmissive areas defining a "bar X" scanning pattern. The "bar X" pattern includes a first bar extending normal to a first direction and second and third bars intersecting with each other to define an "X" pattern. The "X" pattern is disposed symmetrically in relation to the first bar and is positioned in a second direction opposite the first direction from the first bar.
The light beam is scanned in a pattern consisting of a first plane extending through the first bar into the defined scanning region at an acute angle to the panel surface in the first direction, a second plane extending through the second bar into the defined scanning region at an acute angle to the panel surface and at an acute angle to the first direction, and a third plane extending through the third bar into the defined scanning region at an acute angle to the panel surface and at an acute angle to the first direction.
The bar X scanner is capable of accurately scanning UPC code symbols, but is somewhat limited in the range of orientation with which the object bearing the code symbol can be received in the defined scanning region. Although packages having the code symbol on the bottom can be moved quickly through the defined scanning region when the code symbol faces the panel surface no matter how the sides of the package are oriented in relation to the second direction, packages having the code symbol on the side must be more carefully oriented. So long as the spaced parallel bars of a code symbol positioned on a side of a package are vertical when the package is upright, the package can be received in the defined scanning region in a generally upright orientation, with the only concern for positioning being whether the code symbol is generally facing the second direction. However, on some packages the spaced parallel bars of the code symbol are horizontal when the package is upright, whereby the package must be tilted from an upright position when it is moved through the defined scanning region, as well as being oriented to be generally facing the second direction. The different orientations required for packages having vertical vis-a-vis horizontal spaced bar code symbols delays the process of moving the packages through the defined scanning region.
Another prior art system that does not require precise orientation is the so-called Sweda system manufactured by Litton Systems, Inc. This scanning system purportedly is omnidirectional in that the object bearing the code symbol can be oriented in any direction as it is received in the defined scanning region. However, the Sweda system has some "holes" in its scanning pattern where the code symbol cannot be read in certain orientations. Also the depth of field of the Sweda system is such that the code symbol must be received within about 2 to 3 inches of the panel surface. In addition the Sweda system has difficulty in reading symbols with horizontal bars on the side of the received object unless the object is tilted.
Still another prior art system not requiring precise orientation is that which was marketed by Coherent Radiation of Palo Alto, Calif., and was known as the "Coherent Eye". In such a system a light beam is scanned at an acute angle to a reference plane defining a boundary of the scanning region in which the object bearing the code symbol is received. The light beam is scanned in a pattern consisting of a plurality of at least three sets of parallel planes, wherein the different sets intersect with one another. Each scanned plane of light extends into the scanning region normal to the reference plane. The scanning pattern that is impinged upon an object moving through the scanning region is effectively a plurality of adjacent interlocking triangles. Although such system does not require that the object bearing the code symbol be precisely located within the scanning region, if the parallel bars of the code symbol are normal to the reference plane, the code symbol must be oriented to face within a relatively narrow angle of a given scanning direction.